Implement determination of default plugin location for linux/unix systems
Merge branch 'origin/master'

Conflicts:
	source/examples/ViewerQt/main.cpp
	source/gloperate/source/plugin/PluginManager.cpp
Add option to set the search path for plugins
Implement automatic scanning for plugins, supporting an optional search string to omit loading non-plugin libraries
Adjust method names for PluginManager
Merge pull request #5 from hpicgs/plugin_system

Plugin system